Top 25 OSPF Interview Questions & Answers 2021

ospf interview questions

Are you searching for OSPF interview questions? Below, we have mentioned some of the frequently asked interview questions & answers for candidates to get their way and pass the job interview easily.

OSPF Interview Questions & Answers

What do you know about OSPF?

OSPF stands for Open Shortest Path First, which is an open average link-state routing protocol. It’s working is based upon Dijkstra’s SPF algorithm to find the straight paths.

What are the main attributes of OSPF?

The main attributes of OSPF are:

  • Equal Cost Routes management: CEF Load corresponding
  • Protocol Type: Link State
  • Transport: IP (Port89) submit to network walks website
  • OSPF Metric: Cost (Bandwidth)
  • Standard: RFC2328 (OSPFv2), RFC2740 (OSPFv3/IPv6)

How to change the router ID?

In order to change the router ID setting, do the following:

  1. Go to the global config context; the CLI prompt looks similar to the following:

HP Switch(config)#_

  1. If OSPF is not activated, go to Step 3; if OSPF is activated, use no router ospf to deactivate OSPF operation.
  2. Use ip router-id ip-addr to define a new router ID. (This IP address must be unique in the routing switch configuration.)
  3. If you disabled OSPF operation in Step 2, use router ospf to re-enable OSPF operation.

Changing the router ID


ip router-id ip-addr

The ip-addr can be any legitimate, unique IP address.

HP Switch(config)# ip router-id

What are the steps involved in changing neighborships into adjacency?

The steps required are:

  • State Request (LSR) packets, Link State, inform (LSU) packets.
  • Two-way announcement 
  • Database Synchronization which means a switch of Database Description packets, Link
  • After Database synchronization is done, the two Routers are measured as adjacent.

Explain the four routers types?

The four router kinds are:

  • Autonomous System Boundary Routers
  • Internal Routers
  • Area Border Routers
  • Backbone Routers

What are the characteristics of OSPF?

The characteristics of OSPF are:

  • It uses cost as its metric, which is measured based on the bandwidth of the link.
  • It is a classless routing procedure that has support for VLSM and CIDR.
  • OSPF routes have an organisational distance of 110.
  • It comes with no hop-count limit.
  • It provides the feature of creating areas and an independent system.

Describe the functioning and working of various OSPFs?

These are the following steps: 

  • Instead of advertising the reserve to connected networks, OSPF shows the status of straight related links using Link-State Advertisements.
  • OSPF gives the updates when there is a change to one of its links, and will only send the difference through the updation. LSAs are additionally refreshed every 30 minutes.
  • OSPF utilizes the Dijkstra Shortest pathway First algorithm to decide the shortest path.

What is LSA used for inter-area communication? What is the LSA type used for inter protocol communication in OSPF?

Type 3 LSA Is utilised for Inter region communication. For communication with other protocols or external routes, types 4 and 5 will be used.

Can we have one numbered side and leave the other side unnumbered in OSPF?

No, it will work if you have one side numbered and the other hand unnumbered. This makes an inconsistency in the OSPF database that prevents routes from being installed in the steering table.

Tell me some advantages of using OSPF Summarization?

The advantages of using OSPF summarization are:

  • OSPF Summarization reduces the numeral of update messages
  • OSPF Summarization minimizes the quantity of information stored in routing tables
  • OSPF Summarization reduces the weight on Router processor and recollection resources
  • OSPF Summarization reduces the bandwidth practice

Tell me the issues that DR and BDR solve in OSPF?

BDR and DR solve two problems in OSPF:

  • Excessive LSA flooding
  • High No. of Adjacencies

What do you mean by Link state retransmit interval?

OSPF must send recognition of each newly conventional LSA. LSAs are retransmitted until they are approved. The link-state retransmit-interval defines the time among retransmissions. We can utilise the command IP OSPF retransmit-interval to place the retransmit-interval.

What do you mean by OSPF adjacency?

An OSPF adjacency is a theoretical link to a neighbour over which Link State Advertisements can be sent.

Name the five OSPF packet types?

The five OSPF packet types are:

  • DBD
  • LSU
  • LSR
  • LSack

Tell me the purpose of the subnets keyword when redistributing OSPF?

Without the subnets keyword, only primary network addresses that are not straight connected to the router will be redistributed.

  1. Name the few types of LSA?

The few types of LSA are:

  • External LSA
  • Network LSA
  • ASBR Summary LSA
  • Network summary LSA
  • Router LSA

What will happen if we make a priority of an OSPF router as “ZERO”?

OSPF Router with Priority zero will not take part in DR/BDR election.

Tell algorithms OSPF demands, and what is the principle behind it?

OSPF uses the Dijkstra straight Path First algorithm to decide the shortest path and Link-State Advertisements.

Define OSPF timers?

  • Dead Interval: It defines how extended router will wait for hello packets before it declares the neighbour dead.
  • Hello Interval: It defines how frequently the OSPF router will send the hello packet to another OSPF router.

Do you think we can use OSPF without a backbone area?

Yes, but then only intra-area communication is likely. Inter-area communication is not achievable without a backbone area.

Name the Multicast addresses does OSPF use?

OSPF utilize the multicast address of &

Do you think is it possible to have OSPF over a GRE tunnel?

Yes, it is the potential to have OSPF run over a GRE tunnel.

What do you mean by Max age?

Max-Age 1 hour is the period at which a Link-State Advertisement is measured to be outdated.

Define the significance of area 0?

Area 0 is the Backbone Area. All other areas must send their inter-area transfer through the backbone.

What do you know OSPF Router ID?

OSPF Router ID is an identifier that is utilised to recognise the Router. It is a 32-bit number.

So, these are the following interview questions & answers for networking jobs; you can go through these interview questions and clear their job interview efficiently.

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